I noticed a buggy behaviour when trying to insert a special character via a f.e. shortcut "Alt+0235" to get 'ë' in the text.
This character is not placed on the cursor-position, but way down at the bottom of the file.

Confirmed. It does this when num lock is off. When num lock is on, the character inserts in the right place. The insertion with num lock off is very erratic, and extra spaces may also be thrown in freely.

Word wrap doesn't make any difference, or a couple of other variables I checked.

I noticed a buggy behaviour when trying to insert a special character via a f.e. shortcut "Alt+0235" to get 'ë' in the text.
This character is not placed on the cursor-position, but way down at the bottom of the file.

When NumLock is off, you are pressing Alt+Down, Alt+PageDown and so on. Alt key is used to navigate, select text in column mode.